PROJECT SUMMARY Obesity is a significant public health problem, with medical and psychosocial morbidities, impaired quality of life, increased mortality, and substantial health care costs. Up to 30% of treatment-seeking individuals with obesity have comorbid binge eating, an eating disorder behavior characterized by eating a large amount of food and experiencing loss of control. First-line interventions are face-to-face treatments for obesity or binge eating, but current approaches fail to address both conditions and cannot reach all people in need. To tackle comorbid obesity and binge eating, an intervention needs to be designed that: 1) targets both weight and binge eating; 2) improves the efficiency of the intervention while preserving its potency; and 3) is scalable to large populations of users. Thus, I propose a research agenda to design a mobile intervention that targets obesity and binge eating, which aligns with the NIH?s call for research that enhances the precision of intervention delivery. I will conduct two studies with adults with obesity (BMI ?30) and recurrent binge eating (?12 binge episodes in the past 3 months). First, I will employ a user-centered design approach to design a 16- session guided self-help, mobile intervention that combines components of psychological and behavioral weight loss (BWL) interventions. Overvaluation of weight and shape, unhealthy weight control practices, and negative affect are key treatment targets in psychological interventions for binge eating, but are not components of BWL. Thus, I will design an intervention that integrates these three components as adjuncts to BWL. I will conduct usability testing to inform intervention refinements prior to a pilot trial (Aim 1). Second, I will conduct a randomized pilot trial to determine the feasibility of delivering the intervention protocol and to generate preliminary data on the effect of the intervention on changes in weight and binge eating at 16 weeks (post-intervention) and 3 months post-intervention (follow-up) (Aims 2 & 3). I will use a 23 full factorial trial design to randomly assign participants to a combination of the 3 components (n=8 conditions) in order to isolate which of the 3 intervention components are active ingredients. I will apply the Multiphase Optimization Strategy framework to optimize the intervention. These aims support my training plan in which I will receive expert mentorship and training in user-centered design and usability testing (Training Goal 1); using novel frameworks and efficient trial designs (Training Goal 2); and longitudinal data analysis of clinical trials (Training Goal 3). Expertise of the mentorship team, along with the academic and training environment of Northwestern University, will ensure my success. Results of this study will be used to optimize the intervention, which I will then test in a subsequent R01 trial. This K01 Mentored Research Scientist Development Award will equip me with the skills and data to facilitate my career goal of becoming a leader in increasing access to high- quality health care for obesity and weight-related issues, such as binge eating, using scalable interventions.